The fundamental steps of processing color light-sensitive materials generally include a color developing step and a desilvering step. Thus, an exposed color light-sensitive material is introduced into a color developing step, in which silver halide is reduced with a color developing agent to produce silver and the oxidized color developing agent in turn reacts with a color former to yield a dye image. Subsequently, the color light-sensitive material is introduced into a desilvering step, in which the silver produced in the preceding step is oxidized with an oxidizing agent (usually called a bleaching agent), and dissolved away with a silver ion complexing agent (usually called a fixing agent). Therefore, only a dye image is formed in the thus processed color light-sensitive material. In addition to the above described two fundamental steps of color development and desilvering, development processing includes subsidiary steps for maintaining the photographic and physical quality of the resulting image or for improving the preservability of the image. Examples of these steps include use of a hardening bath for preventing a light-sensitive layer from being excessively softened during photographic processing, a stopping bath for effectively stopping the developing reaction, an image stabilizing bath for stabilizing the image, and a layer removing bath for removing the backing layer on the support.
The above described desilvering step may be conducted in either of two ways: a two-step method of separately employing a bleaching bath and a fixing bath; and a one-step method of employing a bleach-fixing bath containing both a bleaching agent and a fixing agent for the purpose of accelerating processing and eliminating labor.
Bleach processing using a ferric ion complex salt (for example, aminopolycarboxylic acid-ferric ion complex salt, particularly iron (III) ethylenediamine-tetraacetate complex salt) as a major bleaching agent is usually employed in processing color light-sensitive materials in view of the need to prevent environmental pollution.
However, ferric ion complex salts have a comparatively low oxidizing power and, therefore, have insufficient bleaching ability.
In order to increase the bleaching ability of a bleaching solution or a bleach-fixing solution containing a ferric ion complex salt as a bleaching agent, it has been proposed to add various bleach accelerating agents to the processing bath.
Examples of such bleach accelerating agents include 5-membered heterocyclic mercapto compounds (described in British Patent 1,138,842), thiadiazole derivatives (described in Swiss Patent 336,257), thiourea derivatives, thiazole derivatives, a 5-membered heterocyclic compound containing two or three nitrogen atoms as ring constituting members and having at least one mercapto group (described in JP-A-54-52534 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")), heterocyclic alkylmercaptan derivatives (described in JP-A-53-32736), disulfide compounds (described in JP-A-53-95630), isothiourea derivatives (described in Research Disclosure, No. 15704 (May, 1977)), and aminoalkylmercaptan derivatives (described in U.S. Pat. No. 3,893,858). Although some of these bleach accelerating agents show a substantially satisfactory bleach accelerating effect, they have various disadvantages. More specifically, when these compounds are added to a bleaching solution and color light-sensitive materials are continuously processed using such a bleaching solution, precipitation occurs in the bleaching solution, which causes many troubles. The precipitate chokes the filters of the circulation system in an automatic processing machine and adheres to the color light-sensitive materials, resulting in stain formation. Further, the bleach accelerating effect degrades under a running condition. This phenomenon is believed to result from the fact that thiol or disulfide is converted to a thiolsulfonate ion by a sulfite ion which crosses over from a developing solution into the bleaching solution and thus loses its ability to adsorb to the developed silver.
Therefore, in order to effectively accelerate silver removal, it is desirable to incorporate such a bleach accelerating agent into the color light-sensitive material instead of adding it to a processing bath such as a bleaching bath or a bleach-fixing bath. However, many compounds which are generally designated bleach accelerating agents form undesired fog when they are directly incorporated into color light-sensitive materials. Moreover, they cause a decrease in sensitivity and a change in photographic characteristics (such as sensitivity, gradation, or fog) and are therefore impractical.
Many attempts have been made to overcome such problems as fog formation caused by the incorporation of a bleach accelerating agent into a color light-sensitive material and to increase further the bleach accelerating effect. For instance, there is a method of using a bleach accelerating agent in the form of a salt (for example, a silver salt) with a heavy metal ion as described in JP-A-53-134430, JP-A-53 147529 and JP-A-55-64237. However, this method does not provide a sufficient bleach accelerating effect. Also known are methods utilizing a bleach accelerator releasing coupler (described in Research Disclosure, No. 11449 (1973) and JP-A-61-201247). However, these known bleach accelerator releasing couplers release bleach accelerating agents only at the time of color development and do not release them at the time of bleaching or bleach-fixing, and thus their bleach accelerating effects are still unsatisfactory. Color light-sensitive materials containing a compound wherein an active group or an adsorptive group of a bleach accelerating agent is blocked are disclosed in JP-A-64-42650. However, these color light-sensitive materials are not sufficiently stable during processing under high temperature and high humidity conditions, although they exhibit bleach accelerating effects. Further improvement, accordingly, has been desired.